The first one known hit Tallon IV, causing the Chozo to die out and corrupt the planet with Phazon. The second known one hit Aether, and considering Aether had an already unstable atmosphere, the strike of the seed created a darker dimension of Aether called Dark Aether. Even the Luminoth in Metroid Prime 2: Echoes say that Dark Aether came only after a 'meteor struck'.